satellites (e.g. of Earth): Their orbits and uses
You can define a satellite as a smaller
object orbiting a larger object and is kept in orbit by the force of
Natural satellites are those
occur naturally in a 'solar system' orbiting a planet.
e.g. our own moon orbiting the Earth,
the many moons of Jupiter.
Artificial satellites are those that we, with our technology,
put into orbit around our moon, the Earth or our other fellow planets e.g.
Mercury, Venus and Jupiter.
When satellites are put into orbit they
are given just the right amount of horizontal velocity so that the resultant centripetal force of gravity keeps the satellite
accelerating in its a
Reminder: Acceleration and
velocity are vector quantities.
The speed of a satellite may
be constant, but it is constant changing in direction, so the
velocity is constantly changing and change in velocity is
acceleration (in this context).
You can vary this horizontal velocity to
position satellites at different distances above the Earth's surface.
Most satellites we launch into space are those that orbit
our own planet Earth - diagram on right of geocentric orbits - an
orbit of anything orbiting the Earth (over 2000 artificial satellites
currently orbiting the Earth).
Artificial satellites can now be sent to orbit other
planets in our solar system and study them in much greater detail than
can be observed by optical telescopes on Earth. You can get much more
scientific knowledge including details on the planet's geology, atmosphere
and weather systems. You can also orbit satellites around our moon and the
moon's of other planets to study them in similar detail.
in polar orbit (orbit 1 on diagram, actually should be lower than
Satellite orbit 1 passes over (or near) both poles, one
after the other in its cycle, and is said to have a polar orbit. It
circles around the Earth at about 90o to the equator.
'Polar satellites' have relatively low
orbits and the Earth rotates under them.
The lower orbit means they have to have a
faster speed (physics above) than geostationary satellites (below) to stay
in orbit which may take as little as a few hours.
Because the orbit time is short and the
Earth rotates within the orbit, they can monitor the whole surface of the
Earth many times in every 24 hours.
Therefore satellites in polar orbit are
used for mapping the landscape, military surveillance (spying!) and producing weather
charts for weather forecasting.
Satellites in a geostationary orbit
(geosynchronous satellites) (orbit 2 on
Satellite 2 travels around in the same direction as the
Earth's spin and at the same angular speed are moving in a geostationary
Geostationary satellites have a high
orbit that takes ~24 hours to go round the Earth (e.g. at a height of 35786
km above the Earth's surface).
This means they keep a constant position
above the Earth's surface because they take exactly one day (23 hours
56 minutes) to complete one orbit.
These geosynchronous satellites are very
useful for continuous communications e.g. radio, telephone and TV
because you can point transmitters and receivers in their direction and they
are stationary relative to each other. Also, the signals can transmitted all
around the globe in a fraction of a second ~speed of light.
They are also used for astronomy e.g.
the Hubble space telescope producing amazing images of distant star
clouds and galaxies - technically it isn't in a geostationary orbit.
On a larger scale, the manned
international space station is effectively a giant satellite performing
all sorts of scientific functions.
INDEX of my physics notes on
Keywords, phrases and learning objectives for astronomy
Be able to describe and explain that artificial satellites
can be put in orbit around a planet like Earth or a moon (like our
Be able to describe the different types of orbits and uses of satellites.